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Introduction

Introduction. Chapter 1. Definition of a Distributed System (1). A distributed system is: A collection of independent computers that appears to its users as a single coherent system. Definition of a Distributed System (2). 1.1.

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Introduction

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  1. Introduction Chapter 1

  2. Definition of a Distributed System (1) • A distributed system is: • A collection of independent computers that appears to its users as a single coherent system.

  3. Definition of a Distributed System (2) 1.1 A distributed system organized as middleware.Note that the middleware layer extends over multiple machines.

  4. Examples of DS • The Internet • Vast interconnected collection of computer network of many different types • Intranets • Portion of Internet that is separately administrated and has a boundary that can be configured to enforce local security policy. • Mobile and ubiquitous computing • Small and portable computing device. • Laptops computers. • PDA, mobiles phone, pagers, video cameras and digital cameras. • Wearable device, such as smart watches • Devices embedded in appliances- hi-fi+washing machine using one “universal remote control”.

  5. Transparency in a Distributed System Different forms of transparency in a distributed system.

  6. Scalability Date Web servers Computers 188 0 1979, Dec. 1989, July 130,000 0 1999, July 56,218,000 5,560,866 • A system is described scalable if remain effective when there is a significant increase in the number of resources and users

  7. Scalability Problems Examples of scalability limitations.

  8. Scaling Techniques (1) 1.4 • The difference between letting: • a server or • a client check forms as they are being filled

  9. Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones.

  10. Lecture 2 Hardware Concepts Multiprocessors Homogenous Multicomputer System Software Concepts Distributed OS Uniprocessor Operating Systems Multiprocessor Operating System Multicomputer Operating System Distributed Shared Memory Network OS Middleware

  11. Hardware Concepts 1.6 Different basic organizations and memories in distributed computer systems

  12. Multiprocessors (1) • A bus-based multiprocessor. 1.7 • Coherent • Incoherent – while using the cache

  13. Multiprocessors (2) • A crossbar switch • An omega switching network 1.8

  14. Homogeneous Multicomputer Systems • Grid • Hypercube 1-9

  15. Software Concepts • DS as resource manager • Provide Virtual Machine to hide the heterogeneous nature of underlying hardware

  16. Software Concepts • An overview of • DOS (Distributed Operating Systems) • NOS (Network Operating Systems) • Middleware

  17. DOS (Distributed Operating Systems) • Multiprocessor Operating System • Manage the resource of multiprocessor • Multicomputer Operating System • Develop for homogenous multicomputer

  18. Uniprocessor Operating Systems • The goal- user and application sharing resources • User mode & kernel mode- Controlled by OS. • Separating applications from operating system code through a microkernel-code for device register, switching between process etc.

  19. Multicomputer Operating Systems (1) • General structure of a multicomputer operating system 1.14

  20. Multicomputer Operating Systems (2) • Alternatives for blocking and buffering in message passing. • Leading to 4 possible synchronization point. 1.15

  21. Multicomputer Operating Systems (3) • Relation between blocking, buffering, and reliable communications.

  22. Distributed Shared Memory Systems (1) • Pages of address space distributed among four machines • Situation after CPU 1 references page 10 • Situation if page 10 is read only and replication is used

  23. Distributed Shared Memory Systems (2) • False sharing of a page between two independent processes. 1.18

  24. Network Operating System(1) • Heterogeneous. • Variety and difference in terms of: • Networks • Computer hardware • Operating system • Programming language • Implementation by different developers • Constructed from a collection of uniprocessor system using own OS. • Connected to each other using computer network.

  25. Network Operating System (2) • General structure of a network operating system. 1-19

  26. Network Operating System (3) • Two clients and a server in a network operating system. 1-20 Generally maintain hierarchical file system. Client can import/mount these file system.

  27. Network Operating System (3) • Different clients may mount the servers in different places. 1.21 #showmount –e <server_name> #mount /mygames <server_name>/private/games

  28. Positioning Middleware • Programs written by different developers cannot communicate unless use common standard • Middleware applied to a software masking the heterogeneity of hardware & software 1-22 General structure of a distributed system as middleware.

  29. Middleware Services • Communication facilities – message passing eg: RPC & Distributed Object Invocation. • Naming- URL still works even the server has been moved. • Persistence – special facilities for storage. • Distributed Transactions- multiple read/write operations atomicaly. • Security – cannot rely on OS only.

  30. Middleware and Openness • In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications. 1.23

  31. Comparison between Systems • A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems.

  32. Clients and Servers • General interaction between a client and a server. • Request and reply behavior. • Connectionless vs connection oriented protocol.

  33. An Example Client and Server (1) • The header.h file used by the client and server.

  34. An Example Client and Server (2) • A sample server.

  35. An Example Client and Server (3) • A client using the server to copy a file. 1-27 b

  36. Processing Level • The general organization of an Internet search engine into three different layers 1-28

  37. Multitiered Architectures (1) • 2 types of machines –two-tiered architecture • client just a dumb terminal(user interface) • Server is handle everything • Alternative client-server organizations (a) – (e). 1-29

  38. Multitiered Architectures (2) • An example of a server acting as a client. • eg: transaction processing – next chap 1-30

  39. Modern Architectures • Multitier Client Server Architecture- • Divide application into 3 components • vertical distribution • Modern Architecture is more consent about the distribution of client and the servers. • An example of horizontal distribution of a Web service.

  40. Summary(INTRODUCTION) • DS: autonomous computer+single coherent system. • Goals • Hardware Concept • Software Concept • Client Server model-application layering • Vertical distribution vs horizontal distribution

  41. Exercise • Do the problems on page 54 and 55. • Eg: #4,#6,#15,#17 • Ask the student in a group to find a journal about the distributed system. Work into group, (5- 6 people) each group. Make a synopsis and give a critique.

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